This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application for Method and Apparatus for Controlling Power for Fusing Roller of Electrophotographic Image Forming Apparatus earlier filed in the Korean Industrial Property Office on Nov. 12, 2001 and there duly assigned Serial No. 2001-70121.
1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus, and more particularly, to a power control method and apparatus for a fusing roller of an electrophotographic image forming apparatus in which an external source voltage is supplied to a heater of a fusing roller to fuse and fix a toner image to a printing paper.
2. Description of the Related Art
Electrophotographic image forming apparatuses include a controller, a power supply unit, a print engine-power supply controller, and a print engine. The controller, which controls the overall operation of a printer system, and converts a print data input from an external unit such as a personal computer (PC) to a drive data suitable for the operation of the print engine and outputs the drive data to the print engine. The controller determines a power mode and controls power consumption of the print engine through the print engine-power supply controller.
The power supply unit receives electric power from an external power source, e.g., commercial-grade alternating-current source, and generates voltages having levels appropriate for operating the constituent units of the electrophotographic printer including the print engine.
The print engine is responsible for substantial printing operations under the control of the a controller. The print engine includes a laser scanning unit for scanning light onto a rotating photoreceptor web or drum to form a latent electrostatic image thereon, a developer for developing the latent electrostatic image into a toner image, a transfer device for transferring the toner image on the photoreceptor web to a printing paper, a fusing device for fusing and fixing the toner image transferred to the printing paper, and an electrostatic charging roller for erasing the latent electrostatic image remaining on the photoreceptor web for initialization to allow formation of a new latent electrostatic image.
For normal printing operation in the print engine, the fusing device needs to be heated continuously to keep its surface temperature to a target fusing temperature at which the toner image can be fused and fixed to a printing paper. For this purpose, the fusing device uses a halogen lamp as a heater source.
The surface temperature of the fusing device is increased to or maintained at the target fusing temperature by ON/OFF (on and off) control of supplying electric power to or cutting off the supply of electric power to the halogen lamp. In particular, electric power is supplied to the halogen lamp to raise the surface temperature of the fusing device from room temperature to the target fusing temperature. Once the surface temperature of the fusing device reaches the target fusing temperature, the supply of electric power to the halogen lamp is cut off. When the surface temperature of the fusing device drops below the target fusing temperature, electric power is supplied again to the halogen lamp.
In the fusing device using such a halogen lamp as a heater source, radiant heat generated by the halogen lamp is transmitted to the surface of the fusing device through the air, so it takes a considerable time to raise the surface temperature of the fusing device from room temperature to the target fusing temperature. Due to low temperature-increasing rate of the fusing device from room temperature to the target fusing temperature, quite a long warming-up time is required.
To compensate for the above problem, a fusing device capable of being heated rapidly from room temperature to a target fusing temperature was developed. Also, power control methods for such a fusing device are disclosed in U.S. Pat. No. 5,627,634 by Koh entitled xe2x80x9cImage Fixing Apparatus having a Heater Energized and Controlled by Electric Energyxe2x80x9d, U.S. Pat. No. 5,907,743 by Takahashi entitled xe2x80x9cImage Heating Apparatus with Control for Phase Control of Alternating Currentxe2x80x9d, and U.S. Pat. No. 5,994,671 by Suzuki et al. entitled xe2x80x9cImage Heating Apparatusxe2x80x9d. These conventional power control methods are applicable to a Canon""s film drive type flash image fixing system (Japan) and can prevent flicker from occurring with reduced power consumption.
A fusing device using a heat pipe having a thermal conductivity a few hundred times greater than silver or copper has been developed. A working fluid is contained in the heat pipe, and the heat pipe of the fusing device is heated through phase changes of the working fluid. Although such a fusing device using a heat pipe has an advantage of reduction in warming-up time for printing, there are problems of temperature overshoot in the supply of power and temperature ripple during a temperature sustain period. Accordingly, a heater of a fusing device is easily damaged with a reduced life span.
To solve the above-described and other problems, it is an object of the present invention to provide a power control method and apparatus for a fusing device of an electrophotographic image forming apparatus in which a temperature overshoot caused by rapidly increasing the temperature of a fusing roller from room temperature to a target fusing temperature and a temperature ripple occurring in the following temperature sustain period can be reduced.
It is another object of the present invention to provide a power control method and apparatus for a fusing device of an electrophotographic image forming apparatus which can prevent the problem of a short life span of the fusing roller caused by damage of a heater of the fusing roller.
To achieve the above and other objects of the present invention, there is provided a power control apparatus for a fusing roller in an electrophotographic image forming apparatus, the power control apparatus including: a fusing roller for fusing toner on a printing paper; a power supply for supplying power to the fusing roller; a thermistor for measuring a temperature of the fusing roller; and a duty controller for controlling a duty ratio of the power supplied from the power supply to the fusing roller by comparing the temperature of the fusing roller measured by the thermistor with a predetermined target fusing temperature. The duty controller changes the duty ratio of the power when the temperature of the fusing roller reaches a first control temperature lower than the target fusing temperature.
The present invention also provides a power control apparatus for a fusing roller in an electrophotographic image forming apparatus, the power control apparatus including: a fusing roller including an inner tube containing a predetermined working fluid for fusing toner on a printing paper; a power supply for supplying power to the fusing roller; a thermistor for measuring a temperature of the fusing roller; and a duty controller for controlling a duty ratio of the power supplied from the power supply to the fusing roller by comparing the temperature of the fusing roller measured by the thermistor with a predetermined target fusing temperature. The duty controller changes the duty ratio of the power when the temperature of the fusing roller reaches a first control temperature lower than the target fusing temperature.
There is also provided a power control method for a fusing roller in an electrophotographic image forming apparatus, the method including: (a) measuring a temperature of a fusing roller; (b) comparing the temperature of the fusing roller measured in the act of (a) with a predetermined first control temperature; (c) changing a duty ratio of the power supplied to the fusing roller when the temperature of the fusing roller reaches the predetermined first control temperature; and (d) supplying power to the fusing roller at the duty ratio changed in the act of (c) until the temperature of the fusing roller reaches a predetermined target fusing temperature.